1. Field of the Invention
The present invention relates generally to treating subsurface liquid reservoirs, particularly oil reservoirs. More particularly, this invention relates to treating these reservoirs to prevent and/or remedy such problems as fouling of extraction wells by scale formation, well corrosion, and souring of oil by bacterial contamination. This invention further relates to treating the liquid in these reservoirs by introducing chemical or biological agents, to affect the properties of the liquid or to aid in the extraction of the liquid.
2. Description of the Related Art
Referring to FIG. 1, a typical undersea oil reservoir has the following morphology. Under the seafloor 10 and a rock dome 12, an oil reservoir 14 is found, usually between a high pressure gas pocket 16 and a layer of water 18.
When a new well is drilled in such a reservoir, oil typically flows spontaneously out of the reservoir as a xe2x80x9cgusherxe2x80x9d, due to the high pressure the oil is under. However, as the well matures and the pressure in the reservoir abates, the gusher subsides and the oil can be recovered only by pumping.
Recovery by pumping, besides being inherently more complex and expensive than getting oil from a gusher, creates several additional problems. Referring to FIG. 2, because water is significantly less viscous than oil, pumping tends to draw the water layer 18 up. This xe2x80x9cconingxe2x80x9d results in a significant amount of water being pumped to the surface. This water cone can even act as a barrier to the oil, forming an immiscible wall between the oil and the well borehole.
The water in an oil reservoir typically contains a large amount of various dissolved salts (e.g., barium sulfate). When the well water leaves the high pressure, high temperature (about 200xc2x0 C.) environment of the reservoir, and travels up the borehole to the ocean floor where the temperature is much lower, these salts tend to precipitate out of the liquid, and deposit on the pipewall as scale. Over time this scale builds up, occluding the well. Periodically, this scale must be removed, typically by the application of an anti-scale agent, applied in a xe2x80x9csqueezexe2x80x9d treatment. These squeeze treatments require shutting down the well for some time, at great expense. After the squeeze treatment, the scale begins to build up again within a short amount of time, necessitating another squeeze treatment within a few months.
Another problem faced during oil recovery is souring, the reduction of sulfates to sulfides in the reservoir oil. This is caused by the introduction of sulfophilic bacteria in the reservoir. Sulfides are highly caustic, and tend to damage well equipment. Sulfides are also extremely environmentally unfriendly, and therefore are undesirable in the recovered oil. Anti-souring agents, especially biocides, are used to control this problem. However, many of these biocides are hydrophilic, and are therefore difficult to introduce into the hydrophobic oil where these bacteria are found.
Other reasons for treating oil in underground reservoirs are known, and other agents for treating underground oil for these reasons are likewise known. For instance, it is sometimes desired to introduce an oxidant into the reservoir somewhat remotely from the extraction well, so that remote combustion can push oil towards the extraction well. Also, because pumping energy requirements increase with the viscosity of the pumped oil, it would be advantageous to treat oil in an underground reservoir to reduce its viscosity.
It would be advantageous to microencapsulate these and other chemical and biological agents for treating oil in subterranean reservoirs, to provide controlled release for any of these purposes. However, pumping places a great deal of stress on microencapsulants, stress that will rupture most microencapsulants. Likewise, the reservoir itself is a very hostile environment, with extremely high pressures, fairly high temperatures, and incredibly caustic chemistries. Moreover, a fully successful encapsulant would need to be compatible with the desired deployment phase, whether the aqueous or non-aqueous phase. Optimally, a single microencapsulant would be adaptable to either environment. Finally, the time scale for release from the microencapsulant should be compatible with the desired treatment protocol. To date, a fully successful microencapsulation scheme for treating oil in subterranean reservoirs has yet to be proposed.
Accordingly, it is an object of this invention to provide long-term treatment systems compatible with various well environments, including water well environments, but especially including petroleum well environments.
It is a further object of this invention to provide long term treatment systems for petroleum well environments, where the treatment includes micro-encapsulation of active agents for delivery to the well environment.
It is a further object of this invention to provide long term anti-souring treatment systems for petroleum well environments.
It is a further object of this invention to provide long term treatment systems for petroleum well environments for preventing scale buildup, on pipe walls and elsewhere in the well.
It is a further object of this invention to provide long term treatment systems for petroleum well environments for preventing the xe2x80x9cconingxe2x80x9d of a water layer under an oil reservoir during pumping.
These and additional objects of the invention are accomplished by the structures and processes hereinafter described.
An aspect of the present invention is a method for delivering encapsulated materials to a subsurface environment, for the treatment of the subsurface environment, having the steps: (a) loading the lumen of hollow microtubules with an active agent selected for treating the subsurface environment, wherein the hollow microtubules are compatible with the subsurface environment; and (b) administering the hollow microtubules to the subsurface environment, thereby permitting the controlled release of the active agent into the subsurface environment.
Another aspect of the invention is a slurry of hollow microtubules, where the lumen of these microtubules is loaded with an agent for the treatment of petroleum well environments, and where these loaded microtubules are dispersed in a liquid phase carrier selected from aqueous carriers, non-aqueous carriers, and emulsions of aqueous and non-aqueous materials.
Another aspect of the invention is a pill comprising a consolidated mass of tubules loaded with one or more active agents, typically bound with a binder.